Sexing tilapia is important, since most farmers wish to cultivate males only. Male tilapias grow bigger and yield a higher profit for aquacultures. The fish is therefore sexed as early as possible and the females are destroyed. Manual sexing of tilapia is tricky and requires specially trained personal. Even experienced personnel will normally get at least 2-5 percent wrong.

When a tilapia fingerling has reached a weight of 25 grams (1 ounce) it can normally be sexed by looking at the genital papilla. The genital papilla is located right behind the anus of the fish. If the genital papilla has one single opening you are looking at a male tilapia. Males have only one opening and both urine and milt will pass through this hole. If the genital papilla has two openings you are looking at a female tilapia, because tilapia eggs do not pass through the same hole as urine. If you find it hard to examine the genital papilla of fingerlings, try placing a drop of dye, such as food colouring or methylene blue, on the genital region. The colour will normally make it easier to distinguish the openings